As centralized power plants fail to meet the growing energy needs worldwide due to outdated grid infrastructure, emissions restrictions, nuclear waste disposal restrictions, and limited availability of traditional coal supplies, the cost and availability of electricity become an issue during peak loads.
Conventional residential and commercial power systems, such as internal combustion, free-piston Stirling, microturbine, fuel cells, and the like, are typically unreliable, require maintenance, or produce noise and pollution when operated. Moreover, it is difficult to move these devices into a house or office because they are large and heavy.
Stirling cycle heat engines have been built and tested since the 1800s, though no major successful product has yet been realized using this core technology. Within the past several decades, the work of Los Alamos National Laboratory (LANL), Palo Alto Research Center (PARC), and the National Aeronautics and Space Administration (NASA), and Nirvana Energy Systems (NES) have advanced this technology through an offshoot called Thermoacoustics. These engines operate utilizing the Stirling cycle to convert heat energy into mechanical energy through means of external combustion or energy harvesting, but are able to operate with fewer moving parts. These devices have promised advancement to the now traditional free-piston Stirling device by reducing complexity and cost. However, typical toroidal thermoacoustic engines have lower efficiency and difficult geometry for high volume manufacturing. These setbacks have been overcome through the work of PARC, NASA, and NES by way of current state of the art technology; electronic feedback thermoacoustic engines. Called “Thermo-Electric-Acoustic Engine” by PARC, “Alpha-STREAM” by NASA, and “Thermo Acoustic Power Stick” (TAPS) by NES, these devices have all used a phase delayed power feedback from an electric-acoustic receiver to drive an electric-acoustic driver. U.S. Pat. No. 8,205,459, U.S. Pat. No. 8,227,928, and patent applications 20110265505, 20110265493, 20130219879 and PCT/US13/24749 describe thermoacoustic devices.
The prior state of the art utilized a capacitor or inductor to phase shift voltage and current as power was collected from the electrical generation end of the device and delivered to the electrical to mechanical side of the device. This phase delay technique is susceptible to the shifting resistive component of the load, as well as additional capacitive or inductive loads that would be added as the device's power was utilized. The control methodology previously utilized, was forced to compensate for alternating current (AC) connections to the grid and other loads in real time in order to maintain stable engine operation.
What is needed is a secure control system for a power system with no hot moving parts that produces electricity for the home and uses waste heat for domestic purposes.